/Engine/Source/Editor/GraphEditor/Public/SGraphPanel.h
Indicate that the connection from the given start to the given end pins is being relinked. A preview connection is being drawn for the relinked connection.
void OnBeginRelinkConnection ( const [FGraphPinHandle](API\Editor\GraphEditor\FGraphPinHandle) & InSourcePinHandle, const [FGraphPinHandle](API\Editor\GraphEditor\FGraphPinHandle) & InTargetPinHandle )